Digital rights management (DRM) has been developed to prevent unauthorized duplication or redistribution of paid contents. DRM applies cryptographic techniques to various contents including documents, MP3 files, ring tones, moving images and games in order to protect the rights of copyright holders. DRM aims to support the full life cycle of digital contents including creation, distribution, usage and retirement.
A DRM-protected content (or DRM content) is encrypted, and only an authorized user can decrypt and use the DRM content. That is, even when a DRM content is duplicated, a user without a valid license cannot use the DRM content. Hence, DRM can prevent illegal duplication of contents.
A license associated with a digital content is issued by a DRM server and sold to a user of the digital content. A license can be stored separately in a user device (a mobile terminal and the like), and can place restrictions on the use of the associated content. In general, licenses can place restrictions in the form of play counts, intervals, timed counts, and accumulations.
A license includes information for restricting the use of an associated DRM content. For example, when a user buys an MP3 file and associated license allowing ten (10) plays, the user can play the MP3 file ten (10) times in total. In this case, whenever the MP3 file is played back, the count is decremented by “1”. When the count reaches zero with repeated playback, the MP3 file can no longer be played back. To continue playback of the MP3 file, the user has to purchase another license for the MP3 file.
In a normal case, when a playback request is issued for a content whose license has expired in a mobile terminal, an alert notifying inability to play is displayed or the cursor or pointer is automatically moved to the next content.
However, DRM contents can coexist with regular non-DRM contents in a mobile terminal. In a typical content list including both DRM contents and non-DRM contents, the user may have difficulty in distinguishing DRM contents from non-DRM contents. This problem tends to worsen as the number of contents increases.
Even in a content list including only DRM contents, the user may have difficulty in distinguishing playable DRM contents from those DRM contents not playable owing to expiration of licenses. That is, existing content listing schemes may fail to distinguish DRM contents having valid licenses from those DRM contents having expired licenses. This may cause inconvenience to the user with regard to management of digital contents.
When the content license expires, the user may decide to purchase another license for the continued use of the content, or may decide not to use the content further and desire to discard the content. In this case, existing content listing schemes may fail to provide information useful for the purchase or discard decision. That is, the user may have to make the purchase or discard decision from memory.
In the case when a content list is composed of contents whose licenses have expired, when the user attempts to play a particular content, the cursor or pointer may simply continue to move to the next content without playback of any content. The user may misunderstand this situation as an error due to abnormal contents or as a failure of the mobile terminal.
Accordingly, it is necessary to provide a means that enables the user to manage a mixture of DRM contents and regular non-DRM contents.